The present invention relates to a connector assembly for armored cable that provides a secure and steady grounding path across the connection for false and other stray voltage.
Providing reliable connections to ground for industrial machinery is vital to the safe and continued operation of that machinery. Should a short circuit or fault condition arise in a piece of industrial machinery, it is all too possible that an operator or maintenance person working on that machine may be injured. In addition, fault conditions in the control system of an industrial machine may cause that machine to malfunction in a way that can cause injury to persons in the vicinity of the machine or can destroy product being processed by that machine.
One method of providing a grounding connection to an industrial machine or other type of device involves connecting a wire between the chassis of the machine or device in question and true ground. This connection may be made using a grounding path formed by a conductive rod driven into the soil and preferably into the water table. Another manner in which a grounding connection is provided to an industrial machine is through the cable that provides power or controlling signals to that machine. This may be accomplished by running an extra conductor through the cable that is connected between the chassis of the device in question and true ground or by forming a conductive sheath around the conductors that form the control or power cable itself.
An example of this former means for providing a ground is the apiaceous three pronged plug used on common household appliances. An example of the latter means of grounding is given in U.S. Pat. No. 5,631,444 to Rook. Rook""s coupling device comprises an inner hollow support body and a separate ground sleeve that is received thereover. The grounding sleeve is sized to be received over the inner hollow support body in a coaxial relationship thereto. Furthermore, the grounding sleeve is sufficiently large that a wire mesh hose formed around an electrical cable may be received therebetween. The grounding sleeve of the Rook coupling is deformed as by crimping so as lock the wire mesh hose of the cable to the inner hollow support body of the coupling. A spring ring is used to rotatively secure a coupling nut to the inner hollow support body of the coupling. Rook does not disclose the formation of a continuous grounding connection from a coupling through the armor of an armored cable. Nor does Rook address how ground currents are to be reliably passed between the male and female components of coupling. Rather, Rook focuses on providing alternative grounding means in the form of lugs that are formed integral with the grounding sleeve. Independent grounding connections are made between the lugs to form the necessary grounding path.
Another shortcoming of the prior art is that heavy conductors of type disclosed in Rook are specifically designed to be assembled in the field by an operator using simple hand tools. While this is useful in that connectors can be assembled where and as needed, forming these connectors by hand results in less than reliable results with respect to the strength and grounding ability of these connectors. Should any of the hand assembly operations be incompletely or incorrectly carried out, the connector may not function as intended and a dangerous fault condition may result.
In industrial control and power supply applications, it is important that a coupling be extremely sturdy so as to physically protect the point at which the electric connections are made within the coupling itself. Failure to protect the electrical connection made within the coupling can result in failure of the coupling and can result in harm to the industrial device that is being controlled or to which power is being supplied or to that device""s operator. One way in which this can occur is if the cable is allowed to bend too near the point at which the electrical connections are made within the coupling. Flexing of the cable tensions the conductors within the cable and can cause the electrical connections to fail. Furthermore, pressure or tension applied to the cord adjacent the coupling as where the cord is step on, bumped or run over by an object such as a fork lift may cause the connectors within a cable to pull away from the electrical connections made within the couple. Another problem with electrical supply and control connections is that the couplings used may themselves be damaged through impact or through the gnawing of vermin such as rats.
In light of the shortcomings of the prior art, it is an objective of the present invention to provide a coupling suitable for use with armored cable that provides an extremely reliable and durable grounding connection through a coupling connection. Another objective of the present invention is to provide a coupling that has a simple structure and is easy to assemble and that rigidly protects the connectors within a cable through the coupling. It is a further object of the present invention to provide a fully shielded and fully insulated electrical connector that can be inexpensively and quickly manufactured. There is yet another object of the invention to provide a coupling that does not rely on a pin and socket connection to form a ground connection through the armor of a grounded cable. Another objective of the present invention is to provide a coupling that is fully armored throughout so as to be impact resistant, impervious to vermin, and preventative of bending stresses that may cause tension on the conductors within a cable to which the couplings are attached. A final objective of the present invention is to provide a cable that can be rapidly, inexpensively, and reliably produced using dependable machine assembly operations.
These and other objectives and advantages of the invention will appear more fully from the following description made in conjunction with the accompanying drawings where like reference characters refer to the same or similar parts throughout the several views.
The objects of the present invention are realized in an armored coupling that has an integral ground connection formed therethrough. This coupling is attached to an armored cable comprising a conductor that is disposed within a conductive sheath.
A substantially rigid sleeve is sized to receive therein the armored cable. The sheath is secured to the cable by at least one set screw that is threaded through the wall of the sleeve and into the conductive sheath of the cable so as form a conduction path from the conductive sheath of the cable through the set screw and into the sleeve. A contact holder is received within a distal end of the sleeve and is constructed and arranged to receive therein the conductor of the armored cable. A substantially rigid jacket is formed over the sleeve and at least a portion of the cable extending from the sleeve. In order to facilitate a strong bond between the jacket, sleeve, and conductive cable, it is preferred to form at least one relief hole through the sleeve so that the material from which the jacket is made can enter between the sleeve and conductive cable to form a unitary structure. A slip ring is received over the sleeve to be longitudinally slidable on the sleeve between a flange extending from the distal end of the sleeve and a shoulder formed by the jacket. The slip ring is fashioned of an electrically conductive material and accordingly extends the conduction path from the sleeve to a coupling nut that is joined to the slip ring.
The armored coupling may be plugged into an outlet or coupling on a machine or may be joined to a mating or complementary coupling. The conductive cable typically comprises a plurality of conductors, though it is envisioned that in high current applications, only a single conductor will pass through the conductive cable.
The present invention may alternatively be characterized as a cable coupling having an integral ground connection formed thereacross. Each half of the coupling has a set screw that is threadedly received within a sleeve received over a first cable. The set screw forms an electrical connection between a conductive sheath of the first cable and the sleeve within which the set screw is threadedly received. A slip ring is received and retained around the sleeve and a coupling nut is secured to slip ring by means of a retaining ridge formed within the coupling nut. The retaining ridge of the coupling nut is received in a groove formed around the slip ring. Note that the retaining ridge and the groove are interchangeable vis-à-vis their relative locations on the slip ring and the coupling nut. The coupling nut is constructed and arranged to mate with a complementary coupling nut on a second coupling, e.g. a male-female coupling arrangement or an outlet of an electrically operated machine. The conduction path for grounding the conductor extends from the conductive sheath of the cable, through the set screw to the sleeve received over the cable, from the sleeve to the slip ring received therearound, and from the slip ring to the coupling nut received over the sleeve and slip ring. Preferably each half of the coupling is provided with a rigid jacket that covers at least a portion of the sleeve and the cable that extends therefrom.
The present invention also embodies a method of forming an armored cable connector that starts with the step of providing a conductor cable having a conductive sheath and at least one conductor housed within the conductive sheath. A predetermined length of the at least one conductor is then exposed.
A substantially rigid conductive sleeve is slipped over the conductor cable and an electrically conductive pathway between the conductive sleeve and the conductive sheath of the conductor cable is created by driving at least one set screw through the conductive sleeve into the conductive sheath. It is preferable to form at least one relief hole through the sleeve prior to its installation. A contact holder is attached to the at least one conductor of the conductor cable for making an electrical connection to a mating conductor cable. Once all of the conductors of the conductor cable have been connected to the contact holder, the plug end of the contact holder is inserted into the distal end of the conductive sleeve.
A rigid jacket is molded over at least a portion of the rigid sleeve and the conductor cable to strengthen the coupling and prevent unwanted tension on the conductors of the conductor cable. A slip ring is next emplaced over the rigid sleeve between the rigid jacket and a flange of the rigid sleeve. It must be noted that the slip ring can be placed over the conductor cable prior to slipping the sleeve over the conductor cable and over-molding the jacket in place.
Finally, a coupling nut is joined to the slip ring such that the coupling nut can mechanically fix the cable connector to a complementary cable connector while providing a reliable electrical connection from the conductive sheath of the conductor cable, through the at least one set screw to the rigid sleeve, and from the rigid sleeve through the slip ring and to the coupling nut joined to the slip ring.